Various methods and apparatus have been developed to provide adjustable resistance to exercise. For example, exercise dumbbells are well known in the art and prevalent in the exercise equipment industry. Generally speaking, each dumbbell includes a handle, and a desired number of weights secured to opposite ends of the handle. The dumbbell is lifted up subject to gravitational force acting on the mass of the handle and the attached weights.
On some relatively advanced devices, the handle or bar is stored in proximity to a plurality of separate weights, and a selection mechanism is provided to connect a desired amount of weight to the handle. Some examples of patented barbell/dumbbell improvements and/or associated features are disclosed in U.S. Pat. No. 4,284,463 to Shields (discloses a dumbbell assembly having opposite end weights that are maintained in alignment on a base and selectively connected to a handle by means of cam driven pins on  the weights); U.S. Pat. No. 4,529,198 to Hettick, Jr. (discloses a barbell assembly having opposite end weights that are maintained in alignment on respective storage members and selectively connected to a handle by means of axially movable springs); U.S. Pat. No. 4,822,034 to Shields (discloses both barbell and dumbbell assemblies having opposite end weights that are maintained in alignment on a shelf and selectively connected to a handle by means of latches on the weights); U.S. Pat. No. 5,769,762 to Towley, III et al. (discloses a dumbbell assembly having a plurality of opposite end weights that are interconnected, stored in nested relationship to one another, and selectively connected to a handle by various means); U.S. Pat. No. 5,839,997 to Roth et al. (discloses a dumbbell assembly having opposite end weights that are maintained in alignment on a base and selectively connected to a handle by means of eccentric cams on a rotating selector rod; U.S. Pat. No. 6,033,350 to Krull (discloses a dumbbell assembly having opposite end weights that are maintained in alignment on a base and selectively connected to a handle by means of selector rods that move in opposite directions to engage weights at respective ends of the handle); and U.S. Pat. No. 6,322,481 to Krull (discloses a dumbbell assembly having opposite end weights that are maintained in alignment on a base and selectively connected to a handle by means of a selector rod that engages different combinations of the weights as a function of its position relative thereto). Despite these advances and others in the field of free weight devices and adjustment methods, room for improvement remains. 